my older brother
Humble term used to refer to one's own older brother when speaking to someone outside the family. The kanji 愚 (foolish) is a self-deprecating prefix common in humble language.
My older brother returned from abroad the other day.
foolish older brother
Literal meaning based on the kanji, but rarely used as a standalone insult. More often encountered as a self-deprecating humble reference (sense 1) or in literary contexts.
My older brother currently lives in Osaka.
He lamented that the family business had declined because of his foolish older brother.
foolish older brother and smart younger brother
Formed from 愚 “foolish” and 兄 “elder brother.” 愚 is either literal or a self-deprecating element used when referring humbly to one’s own family member.